Climate: New study slashes estimate of icecap loss

Sep 07, 2010 by Richard Ingham

Estimates of the rate of ice loss from Greenland and West Antarctica, one of the most worrying questions in the global warming debate, should be halved, according to Dutch and US scientists.

In the last two years, several teams have estimated Greenland is shedding roughly 230 gigatonnes of ice, or 230 billion tonnes, per year and West Antarctica around 132 gigatonnes annually.

Together, that would account for more than half of the annual three-millimetre (0.2 inch) yearly rise in sea levels, a pace that compares dramatically with 1.8mm (0.07 inches) annually in the early 1960s.

But, according to the new study, published in the September issue of the journal Nature Geoscience, the ice estimates fail to correct for a phenomenon known as glacial isostatic adjustment.

This is the term for the rebounding of Earth's crust following the last Ice Age.

Glaciers that were kilometers (miles) thick smothered Antarctica and most of the northern hemisphere for tens of thousands of years, compressing the elastic crust beneath it with their titanic weight.

When the glaciers started to retreat around 20,000 years ago, the crust started to rebound, and is still doing so.

This movement, though, is not just a single vertical motion, lead researcher Bert Vermeersen of Delft Technical University, in the Netherlands, said in phone interview with AFP.

"A good analogy is that it's like a mattress after someone has been sleeping on it all night," he said.

The weight of the sleeper creates a hollow as the material compress downwards and outwards. When the person gets up, the mattress starts to recover. This movement, seen in close-up, is both upwards and downwards and also sideways, too, as the decompressed material expands outwards and pulls on adjacent stuffing.

Often ignored or considered a minor factor in previous research, post-glacial rebound turns out to be important, says the paper.

It looks at tiny changes in Earth's gravitational field provided by two satellites since 2002, from GPS measurements on land, and from figures for sea floor pressure.

These revealed, among other things, that southern Greenland is in fact subsiding, as the crust beneath it is pulled by the post-glacial rebound from northern America.

With glacial isostatic adjustment modelled in, the loss from Greenland is put at 104 gigatonnes, plus or minus 23 gigatonnes, and 64 gigatonnes from West Antarctica, plus or minus 32 gigatonnes.

These variations show a large degree of uncertainy, but Vermeersen believes that even so a clearer picture is emerging on icesheet loss.

"The corrections for deformations of the Earth's crust have a considerable effect on the amount of ice that is estimated to be melting each year," said Vermeersen, whose team worked with NASA's Jet Propulsation Laboratory and the Netherlands Institute for Space Research.

"We have concluded that the Greenland and West Antarctica ice caps are melting at approximately half the speed originally predicted."

If the figures for overall sea level rise are accurate, icesheet loss would be contribute about 30 percent, rather than roughly half, to the total, said Vermeersen. The rest would come mainly from thermal expansion, meaning that as the sea warms it rises.

The debate is important because of fears that Earth's biggest reservoirs of ice, capable of driving up ocean levels by many metres (feet) if lost, are melting much faster than global-warming scenarios had predicted.

In 2007, the UN's Intergovernmental Panel on Climate Change (IPCC) predicted oceans would rise by 18-59 centimeters (7.2 and 23.6 inches) by 2100, a figure that at its upper range means vulnerable coastal cities would become swamped within a few generations.

The increase would depend on warming estimated at between 1.1 and 6.4 degrees Celsius (1.98-11.52 degrees Fahrenheit) this century, the IPCC said. It stressed, though, the uncertainties about icesheet loss.

More information: This research has been published in the September issue of Nature Geoscience (Nature Geoscience 3, 642 - 646 (2010)). It has also been prepublished online: www.nature.com/ngeo .
Also see 'Sea-level rise: Ice-sheet uncertainty' in de News & Views section in this edition of Nature Geoscience (Nature Geoscience 3, 596 - 597 (2010)) for editorial comments upon the article.

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User comments : 27

"... the ice estimates fail to correct for a phenomenon known as glacial isostatic adjustment."

but it did include the "we like these original results, more funding" bias. Global Warming has set back scientific reputation a long way with the general public. Thanks, "the debate is over" Al. Take that hockey stick and shove it where....

Right, I keep forgetting that scientists are only out to make money and keep there jobs right. We can only trust oil men, who are only out to help and teach the public, right.

If scientists are only out to make money, why on earth are you folks even reading about this or trying to debunk global warming. I mean, scientists are curropt, therefore you cannot base any of your conclusions on science, only belief... right? Am I missing something? I mean really. You think the science has been so curropted, so what the hell are you basing your beliefs on? Intuition?

Interesting result--particularly since it implies that not just glacial melt, but the thermal expansion of the oceans has been poorly estimated. Do the implied rates of thermal expansion for the oceans match what would be expected, considering the oceanic temperature trend? Does anyone happen to know whether it's possible to estimate the rate of thermal expansion we should be seeing, based on the observed change in ocean temperatures?

...Also, dtxx, how is this moving the goalposts? This team noticed a problem, and attempted to provide a correction (whether they're successful or not, of course, remains to be seen). Would you have been happier (and less likely to impute the results to intellectual dishonesty/clumsiness) if they had found that melt rates had been underestimated?

If scientists are only out to make money, why on earth are you folks even reading about this or trying to debunk global warming.

If people want to make money they go to business school, or become medical doctors. Scientists are driven by a need to understand the universe, and everything in it.

The scientific method has proven to be a very powerful tool in developing that understanding. But laymen seem to think that the key part of the scientific method is testing hypotheses. It is not. The most important part is a mindset of questioning everything, including the conclusions of that paper you just spent three years working on. In fact, "trashing" the work you have been doing tends to lead to Nobel prizes, if you discover some residuals in your data that point to new physics, or chemistry, or whatever.

So treating all new results as subject to question instead of Holy Writ, is what scientists do. Contrasting to other results to find discrepancies? The same.

If scientists are only out to make money, why on earth are you folks even reading about this or trying to debunk global warming. I mean, scientists are curropt, therefore you cannot base any of your conclusions on science, only belief... right? Am I missing something? I mean really. You think the science has been so curropted, so what the hell are you basing your beliefs on? Intuition?

You really think that all scientists are pure as the driven snow? Do you know so LITTLE about human nature? Scientists are people first and foremost, and just like other people, yes, they're out to make money...no surprise there.

Does this invalidate all AGW research? Of course not. Are we right to suspect motives of such research when there's a lot of money riding on the line? Most certainly we are, and will continue to do so, despite the naivety of others.

That's fine, I can agree with that. The problem is that I find ignorant people only use that saying when the science doesn't support their arguement, yet ignore it when it does. Generally, these people don't even read the science, instead, they read the headline and post a comment when it doesn't agree with their BELEIFS saying the scientists are curropt with zero proof to back it up. Extreme claims like this require extreme proof.

Most of the time people who think global warming is false simple state ALL science is curropted, therefore we cannot trust AGW science. Fact of the matter, you have to look at who has the most to gain or lose. Scientists don't own these green technologies, corporations do... so, first and foremost, put any curroption blaim on the companies. Second, oil companies obviously have the most to lose.... If your going to put the curroption label on someone without proof.

Fact of the matter, you have to look at who has the most to gain or lose.

Who has been gaining? Al Gore and those sellin carbon credits?Enron and BP were huge supporters of Kyoto.If scientists are useful idiots for these shysters, then they deserve some blame and need to take responsibility for their actions and take control of the message.

A very interesting article and equally interesting responses. First an observation. Those who have been talking about how we can't trust the models are now believing this model. Even though I do trust the models I also think this one has merit and helps make the other models better.

Second. Did anyone notice the sentence above: "The debate is important because of fears that Earth's biggest reservoirs of ice, capable of driving up ocean levels by many meters (feet) if lost, are melting much faster than global-warming scenarios had predicted." Let me explain that sentence if you didn't get it. The existing models were showing ice melt to be lower than measurements were indicating. The new research shows the models were closer to right than anyone thought because it also shows lower ice melting rates and it shows that the gravity measurements were probably skewed. Now the testing of these predictions starts. However, it strengthens the plausibility of existing models.

-What? Al Gore? Really? From what? Book Sales? Really? You really think Al Gore is lying about the evidence he assembled from multiple studies to sell a book? Really? Come on man. He's been rich as hell for a long time, book sales aren't his bread and butter.-Those selling carbon credits? Really? REALLY!? Do you even know who sells carbon credits? Carbon Producers you moron! They are dished out on a percapita basis by the governemnt for free to only the most massive carbon producers, if they have any left over, they sell them for a small profit. If anyone, you should point the finger at mfrs of pollution controls.

Enron and BP were huge supporters of Kyoto.

-if you really think that your dumber than you look.

If scientists are useful idiots for these shysters, then they deserve some blame and need to take responsibility for their actions and take control of the message.

Look at the bigger picture. From techno-dimwit Al "no debate" Gore promoting a fraudulent hockey stick model to the UN IPCC relying on bogus anecdotal data collected by a weekend backpacker and top researchers bragging about "hiding the temperature drop data", the scientific community has allowed itself to become subservient to political agendas and earned diminished credibility. It's not only the tawdry AGW debacle, but corn to ethanol and many other issues. It's a very sad trend for society that science policy is increasingly driven by money and power, not knowledge.

"Critics, mostly on the political right and among global warming sceptics, say Mr. Gore is poised to become the world's first "carbon billionaire," profiteering from government policies he supports that would direct billions of dollars to the business ventures he has invested in. "http://www.telegr...ire.html"Amidst the talk about the benefits that Kyoto Protocol is sup-posed to promote, it is perhaps forgotten especially amongst the greenies how Kyoto was born in the corridors of very big business. The name Enron has all but faded from our news pages since the company went down in flames in 2001 amidst charges of fraud, bribery, price fixing and graft. But without Enron there would have been no Kyoto Protocol."http://www.freere...29/posts

"But the Kerry-BP alliance for an energy bill that included a cap-and-trade scheme for greenhouse gases pokes a hole in a favorite claim of President Obama and his allies in the media — that BP’s lobbyists have fought fiercely to be left alone. Lobbying records show that BP is no free-market crusader, but instead a close friend of big government whenever it serves the company’s bottom line.

While BP has resisted some government interventions, it has lobbied for tax hikes, greenhouse gas restraints, the stimulus bill, the Wall Street bailout, and subsidies for oil pipelines, solar panels, natural gas and biofuels.

I read or skimmed it all marjon. You see Al Gore as a man investing in something, then dishonestly hyping it up to increase his asset value, I see a man investing in what he beleives in. I do the same. I'm investing in hydrogen/electric car companies and supporting companies simply because, I beleive, if these industries do not skyrocket to success, money will end up being worthless... save the planet or economy and profit are pointless, and I do think the danger is real.

Didn't have time to read the whole ENron article, but I'm not surprised at all. These companies, for YEARS, have been pushing the unworkable, the delayable and the impracticle. ENRON pushing carbon accounting, originally rolled out slowly over 50 years and 100% vulentarily, isn't surprising.

Greenies are sometimes forced to take these intentionally unworkable ideas and make them workable because these companies push back way to hard on anything workable. They like to maintain the appearance of caring, yet do..

I read or skimmed it all marjon. You see Al Gore as a man investing in something, then dishonestly hyping it up to increase his asset value, I see a man investing in what he beleives in. I do the same. I'm investing in hydrogen/electric car companies and supporting companies simply because, I beleive, if these industries do not skyrocket to success, money will end up being worthless... save the planet or economy and profit are pointless, and I do think the danger is real.

Spin it any way you want if it makes you feel better.But, recall, Gore was a senator and a VP who apparently used his office for personal gain.If you find that acceptable why shouldn't scientists do the same?

While BP has resisted some government interventions, it has lobbied for tax hikes, greenhouse gas restraints, the stimulus bill, the Wall Street bailout, and subsidies for oil pipelines, solar panels, natural gas and biofuels.

Because BP already conforms to higher standards set by the British Government, giving them a competitive edge. You have a problem with people trying to make money? I thought you were a free marketeer.

Spin it any way you want if it makes you feel better.But, recall, Gore was a senator and a VP who apparently used his office for personal gain.If you find that acceptable why shouldn't scientists do the same?

I'm not spinning anything, just making it clear to everyone the differences in interpretation between me and you... If I am spinning, which i'm not, so are you.

Eventually, even the most fanatical AGW doomsayers will have to come up with a theory to explain why we are all still alive.

this clearly shows your ignorance on the subject brother. No GW models predict that all humans should be dead RIGHT NOW, so what hell are you talking about?

gunslingor, mosahlah did say eventually, maybe he is taking a very long term view.

I do have to take issue with some of marjon's comments though. Governments and big business enjoy doing business with each other because it is easy. Very easy for a gov. to legislate something that the big businesses can enforce for them. (Probably the main reason the enjoy bailing out big banks instead of small investors.) Like big business government is happier dealing with big unions than dealing with individuals one of the reasons why unions have a favourable status in many countries (it is so much easier for government).

Personally, I think it is wrong to promote big companies and unions at expense of the individual but that is big government for you.

Not sure why oil companies are so down on new technologies as they have the money and resources in general to profit the most. Government likes to get taxes with least effort hence the PAYE (pay as you earn tax system).

cont. growing businesses need stability. The use of tax incentives that help grow solar and wind farms and electric car sales are wonderful ideas but government is all about getting elected and they seem to have no idea that they are supposed to provide a stable environment to promote growth in the industries they want to grow.

Emphasis here should be on the word stable. For a government that might mean three years, for a new business model it means more like 10 to 15 years.

Not sure why oil companies are so down on new technologies as they have the money and resources in general to profit the most.

-I agree, took a long time for me to finalize my speculation as to why they resist making more money... I think it comes down to control. Fossil fuels are distributed, but production and processing is centralize giving them total control over society. So, I think they are afraid of lossing that control when every house has solar cells, wind turbines and electric cars. I think it's all about fear, fear of lossing their power, people ion the US today, especially CEOs and VPs, seem to be far more interested in absolute stability than growth and improvement.

MARJON,

I just can't beleive your really sitting here pointing the conflict of interest arguement at Al Gore with all the oil men running this country. Did you have the same problem when Bush was elected, an oil man? Do you have a problem with oil companies paying each congressman millions?

I'm glad you agree, the conflict of interest is there and has been for decades.

I realize you don't beleive the science of GW for whatever strang reason, but you also must consider the health consequences. If you cannot reconcile your beliefs with the hard science of AWG, just focus on the millions dieing each year from pollution.

Anyway you look at it, we have far better solutions for owr energy needs than fossil fuels. I dare you to challenge or agree with that.

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